production on the majority of 20 series cards finished the middle of last year to make way for the incoming 30 series cards, I think the 2060 was the onlyexception, and that will probably go soon with the launch of 3060 later this month
As Martin said, mostly because of the 3000 series cards that were newly released. Older gen GPUs will lower in stock to make way for the newer generation GPUs, and soon Nvidia will focus on the 3000 series GPUs as there have been leaks of more of them to come, including more budget ones. The slowed down production in the 1600 and 2000 series cards have also probably slowed down to help with stocks since as you can see, they’ve been struggling with stocks from the day of release with the 3000 series GPUs.